A toner which contains a color developable compound and a color developing agent and can be decolorized is known. When an image is formed using this toner, by heating the printed paper at a temperature between 100 and 200° C. for about 1 to 3 hours, a printed region can be decolorized. The paper in which the printed region was decolorized can be reused, and therefore, this technique can contribute to a decrease in the environmental load by reducing the consumption of paper.
This decolorizable toner can be produced by, for example, melt-kneading a color developable compound and a color developing agent along with a binder resin through a kneading pulverization method, thereby incorporating the color developable compound and the color developing agent in the inside of the toner. However, when a kneading pulverization method is used, kneading is performed at a high temperature between about 100 and 200° C. under a high shearing force, and therefore, a leuco dye (a color developable compound) and a color developing agent are uniformly dispersed in a binder resin, and a reaction between the leuco dye and the color developing agent is inhibited, resulting in decreasing the developed color density of the toner. Further, when a toner material such as a binder resin or a release agent has a decolorizing action, the developed color density of the toner is decreased at the time of kneading in the same manner. Therefore, it is necessary to select a material having a low decolorizing action as a toner material. In particular, as the binder resin, only a specific resin having no decolorizing action such as a styrene-butadiene resin can be used, and it is extremely not easy to use a polyester resin or a styrene acrylic resin having an excellent fixing property because such a resin is liable to exhibit a decolorizing action.
On the other hand, as a production method other than the kneading pulverization method, there is a method for obtaining a toner by, for example, a suspension polymerization method. In this method, however, a leuco dye and a color developing agent are mixed as such with a monomer. Therefore, the method has a problem that if a monomer having a polar group such as a carboxylic acid or a carboxylate ester is used, a color developing reaction between the leuco dye and the color developing agent is inhibited to decrease a developed color density. Accordingly, only a specific monomer which does not inhibit the color developing reaction can be used, and it is not easy to use a monomer with which a binder resin having an excellent fixing property is formed even when a toner is produced by a suspension polymerization method.